The present invention relates to improvements in image-stabilizing apparatus of the type used in optical instruments, such as still and cine cameras, for minimizing image smear, as might result, for example, from an unsteady hand of the instrument user.
Numerous devices have been proposed heretofore for stabilizing an image formed at the image plane of an optical instrument. Such devices typically comprise some type of mounting mechanism for angularly decoupling the image-forming lens from the instrument housing. Upon being angularly decoupled from the housing, the lens and the image formed thereby can remain relatively stable while the housing undergoes certain random and relatively high frequency angular changes in pitch and yaw. It is this type of angular movement of the instrument housing (cf. with lateral movement, in the image plane, or a roll or translational movement of the housing about or along the optical axis of the lens) which accounts in major part for image smear.
Many image-stabilizing devices are relatively complex, employing electronic circuits, gyroscopes, complex optical systems, etc. to steady the position of the image-forming element. See, for example, the disclosures of U.S. Pat. No. 3,953,106 issued to Furukawa; U.S. Pat. No. 3,892,467 issued to Shin; and U.S. Pat. No. 3,845,929 issued to Reekie et al. Other less sophisticated devices, such as disclosed in U.S. Pat. No. 3,728,948 issued to Fraser, tend to produce an undesired distortion or defocusing of the stabilized image. The Fraser device, like many image-stabilizing devices, comprises a lens mount by which the lens is mounted for gimbal movement about a point where the optical axis of the lens intersects its focal plane. While this mounting arrangement angularly decouples the instrument housing from the image-forming lens, it allows the focal plane of the lens to tilt relative to the image plane of the instrument (i.e. the plane at which images are desirably formed, such as the film plane when the optical instrument is a camera, or the focal plane of the eyepiece when the optical instrument is a telescope or the like). This tilting acts to produce a defocused image at the instrument's image plane which worsens with displacement from the center of the image plane.
In addition to the complex mechanisms and/or the defocusing problems which characterize conventional image-stabilizing devices, most such devices comprise relatively massive components and/or low-force springs to reduce the resonant frequency of the lens mount so that it resists an instantaneous return of the lens from an unbalanced condition to a balanced condition. See, for example, the disclosures of the aforementioned U.S. Pat. Nos. 3,728,948 and 3,892,467. These massive components and springs add considerably to the weight, size and mechanical complexity of the device, making it difficult to incorporate in relatively small and/or inexpensive optical instruments.